Billet mill wherein the rolling gap is controlled during the penultimate pass and fixed during the final pass



Sept. 23, 1969 K. A. YEOMANS 3,468,145

BILLET MILL WHEREIN THE ROLLING GAP IS CONTROLLED DURING THE PENULTIMATE PASS AND FIXED DURING THE FINAL PASS Filed June 16, 1966 3 Sheets-Sheet 1 Aemvsr/l 41mm YEOMAMS Sept. 23, 1969 YEQMANS 3,468,145

BILLET MILL WHEREIN THE ROLLING GAP IS CONTROLLED DURING THE PENULTIMATE PASS AND FIXED DURING THE FINAL PASS Filed June 16, 1966 3 Sheets-Sheet, 2

DES/RED FINAL OUTPUT L FUR we T SPECIFIED DES/RED 2. 1a WIDTH our ur w r M 74 3 76 \NvEN'roR KEN/var 4; FRED Ysamms ATTORNEYS stpt. 23, 1969 Y oM s 3,468,145

BILLET mm. "HEREIN THE: ROLLING GA? 15 commons DURING THE PENULTIMATE PASS AND FIXED DURING THE FINAL -PAss Filed June 16, 1966 3 Sheets-Sheet 5 22 @25 25 25 L G) rfi M 1 I F J I Lj 21 K) ,4 I 23 .4

2 8 FURTHER SPECIFIED INFORMATION REUU/RED F/N/SHED SIZE FIG. 7.

INVENTQQ KEN/v5 TH 141. FRED Yam/m5 A'r-roanms United States Patent O US. Cl. 72-12 9 Claims ABSTRACT OF THE DISCLOSURE A mill for producing stock having a desired crosssection in at least two passes. The roll gap of a mill stand is maintained substantially at a predetermined value during the final pass and the roll gap is controlled during the penultimate pass to produce stock of an intermediate cross-section which bears a predetermined relationship to the roll gap of the final pass whereby stock of the desired cross-section is produced.

This invention relates to rolling and concerns a method and apparatus for automatically controlling the rolling of relatively thick metal stock in accordance with a predetermined relationship between the cross-section of the stock before and after rolling to produce stock having a cross-section substantially the same as a desired crosssection. In this respect it should be understood that thick stock encompasses material in billet, rod, bar, or like form which generally has thickness of the samegorder as width, as distinct from strip, plate and sheet material where the thickness is relatively small and of an order" of magnitude lower than the width.

In one aspect, the invention provides a method of rolling stock involving subjecting the stock to at least two passes for producing stock on the discharge side of the last of the two passes having a cross-section substantially the same as a desired cross-section, the method comprising controlling the roll gap of the penultimate of the two passes so that stock will be presented to the last of the two passes having such a cross-section compared with the roll gap of the last of the two passes that the stock discharging from the last of the two passes has a crosssection substantially the same as said desired cross-section.

In another aspect, the invention provides a rolling mill having means providing at least two passes for producing stock on the discharge side of the last of the two passes having a cross-section substantially the same as a desired cross-section, the mill further having control means for controlling the roll gap of the penultimate of the two passes so that stock will be presented to the last of the 3,468,145 Patented Sept. 23, 1969 stock during a sequence of passes through one or more mill stands, which comprises automatically controlling the roll gap setting of the relevant stand for one pass of the sequence, other than the last, in response to a predetermined relationship between ingoing stock cross-sectional shape immediately prior to said pass, the outgoing stock cross-sectional shape produced by said pass, and the spread of the stock during said pass transversely of the pass line, to produce outgoing stock section of substantially predetermined form from the pass next succeeding that under automatic control.

Application of the present invention may be of predictive and/ or feedback control form.

In order that the present invention may be clearly understood and readily carried into effect, the same will now be more fully described, by way of example, with reference to the accompanying drawings. FIGURES 1 to 4 graphically illustrate the basis of the invention, while FIGURES 5 to 7 diagrammatically illustrate apparatus employing the invention. FIGURE 5 illustrates a reversing mill, while FIGURES 6 and 7 illustrate multi-stand mills.

Considering first the case of rectangular section stock, such material is deformed not only by vertical reduction but also by horizontal spread when passed through parallel horizontal rolls set with a gap less than the ingoing stock thickness. Spread varies with the reduction that is taken, with the height/width ratio and with the diameter of the rolls. Other factors, for example, tension, are also relevant, but, in any event, for a particular rolling situation the relevant factors are effectively fixed and for a particular ingoing stock section there exists a unique relationship between the reduction and spread as indicated by FIGURE 1. In FIGURE 1 the characteristic OP defines the range of outgoing sections, in terms of reduction AH and spread AB relative to an origin 0 representing the ingoing height A and width B, which can be obtained with variation of the roll gap and, thereby, height. Thus, the origin 0 represents rolling with a gap greater than or equal to the ingoing stock height whereby no reduction or spread occurs, while as the roll gap decreases reduction and spread occur to produce a section (AAH) (B-l-AB).

If the stock section varies from the aforementioned given section, different characteristics results as indicated in chain line, and it will be seen that the various characteristics are non-coincident.

Similarly, a required stock section can be rolled from a unique range of ingoing stock sections without changing the roll gap and which range can be represented by a characteristic curve such as OP in FIGURE 2, but with the origin 0 now representing required section A B produced by reduction AB and spread AH from ingoing stock section (AAH) (B+AB).

Considering now the rolling of rectangular stock to a required section, it will, of course, be unusual for the ingoing stock to have a section lying within the unique curvilinear range such that the required section can be produced in a single pass. However, the required section can be produced within two passes, normally the last and penultimate of the usual sequence of reducing passes. The manner in which this is achieved is illustrated 3 graphically by FIGURE 3 which effectively combines the characteristics of FIGURES 1 and 2.

Briefly: point P represents the stock section A B immediately prior to the penultimate pass and the curve therethrough represents the unique range of sections which can be rolled from such stock as in FIGURE 1. The origin represents the required stock section AXB and the curve therethrough represents the unique range of ingoing sections for the last pasS which can result in the required section as in FIGURE 2. The two curves then have a unique intersection P which represents the section A B to be produced by the penultimate pass whereby the last pass can produce the required section.

Thus, taking account of the fact that the successive passes in rolling thick stock are conventionally carried out with mutually perpendicular rolling planes relative to the stock, the penultimate pass should be rolled with a roll gap setting to produce a reduction AA and spread AB such that A AA =A and B +AB =B and the ultimate pass should be rolled with a constant gap to produce a reduction AB and spread AA such that A +AA =A and B AB =B. For a different starting section represented by P a diiferent intersection P is relevant and correspondingly different rolling is possible to produce the required stock section.

It is important to appreciate then that the required stock section is produced by one pass with a predetermined rolling gap by controlling the roll gap setting of the preceding pass to produce an intermediate section for presentation to the second pass which intermediate section will roll to the required product section with the predetermined rolling gap. Effective fixing of the second pass rolling gap will be produced directly by the roll gap setting in most mill forms relevant to the present invention, since billet, rod and such like mills are normally stiff, that is to say they do not exhibit significant spring or stretch during rolling. However, if the rolling gap does not correspond sufiiciently to the actual setting to give a desired accuracy, then automatic control devices of similar form to those employed for strip gauge control can be used to maintain the rolling gap at a substantially predetermined value.

A further point to note is that the reductions taken should not be so large as to give rise to significant bulging of the section sides.

Automatic control of rolling to produce a required rectangular section, as above, in two passes can be achieved then by a predictive control system on the basis of the ingoing sectional measurements of the stock for the first of the two passes and predetermined expressions or characteristics relating reduction and spread as produced by the mill stand or stands through which the passes are to be made. This can be achieved by use of a variety of theoretically produced relationships for reduction and spread or by relationships derived empirically with trial passes.

Also, while the above more particular discussion has been concerned with rectangular sectioned stock, it is equally relevant to other sections as produced in so-called shaped passes, although the question of spread is more complex since the reduction will not be constant across the stock and the spread is consequently influenced by longitudinal shear effects. The significance of this complication is that the spread, and hence the eifective reduction in sectional area depends on the profile of reduction and is not related to ingoing height and width in a simple manner in a shaped pass.

Nevertheless equivalent rectangular sections can be derived and used for the purpose of spread calculations in relation to shaped passes. In any event, even if simple analytical relationships such as those of FIGURES 1 and 2 cannot be formulated, there will be a range of sections which will fill any given shaped pass and this is illustrated by example in FIGURE 4 with reference to rectangular sectioned stock entering an oval pass. It will be noted that the entered section must be of a height at least equal to the height of, and at least equal area to the required oval. The relationships previously referred to may be determined empirically.

Similarly, the curvilinear ranges will exist for other shapes of ingoing stock as may be produced by a preceding pass and a particular case of interest is that of the diamond-square sequence. For a particular size of stock entered into the diamond pass, a range of diamond shapes of different degrees of fill may be obtained by varying the roll gap; and, for the square pass, there is a range of diamonds produced by different gap settings and each with a respective width that can give an accurate product. Then, as with rolling rectangular sectioned stock, between parallel rolls, the diamond pass gap can be controlled to give an intermediate diamond product which can, in turn, be rolled to the required square dimensions.

However, in practice the scope for control will probably be more restricted in shaped passes and this may lead to a requirement for automatic control on preceding passes or restriction of the number of unregulated preceding passes.

It should be appreciated, in any case, that the present invention is not intended to be limited to control of passes at the end of a sequence, but can equally well find application in circumstances where accuracy of an intermediate product is important.

Turning now to the question of practical application of the invention, reference has already been made to a purely predictive system. However, other systems are possible and may be of feedback, or composite predictive and feedback form.

In a simple feedback control system variation of outgoing stock section relative to required section for one stand of a continuous mill can be used to control the roll gap of the preceding stand, the gap in said one stand being maintained to give the required section for correctly presented section. Thus, the error in output section width will be arranged to reduce the controlled stand gap in the event of an increase of the fixed stand product, and vice versa.

Returning to the earlier mentioned predictive control system, this is advantageously applicable to reversing mills in addition to continuous mills. However, while this system predicts specific gap settings for the relevant pair of passes, it is important that the passes be presented with stock of uniform section along their length. To avoid this restriction, it is desirable to monitor the section produced by the first controlled pass and to effect a feedback correction in response to variations from the section required of the predictive system for the final pass.

Again in predictive systems as applied to continuous mills it may be desirable to monitor the section produced by the second pass to update the relationships on which the predictive control of the preceding pass is based.

Turning to FIGURE 5, there is shown stock 10 going through the penultimate pass of a reversing mill 11 the screwdown setting of which is adjustable and under the control of a controller 12. A gauge 13 of known type measures the height and width of the stock coming out of the mill. Into the controller 12 are fed information concerning the desired final stock output from the last pass of the reversing mill; the height and width measurements as given by gauge 13; information relating to the nominal size of the material prior to rolling; the diameter of the rolls of the penultimate pass; the spread coeflicient of the rod.

With each rolling sequence, or pass, there is associated a set of correct values for the dimensions of the stock leaving each pass. To produce an accurate final section, the deviations of the height and width of the material rolled from the penultimate pass must obey a relationship which may be represented by a linear equation in which the mathematically weighted values of the errors in height and width sum to zero or a constant value. The

controller 12 is arranged to so modify the screwdown of the mill 11 during the penultimate pass that a section in accordance with this relationship is obtained. The Weighting of the errors may be determined empirically instead of mathematically. The controller 12 may take the form of a digital analogue computing machine of known type which is programmed with the weighting of the errors in height and width.

The stand 11 may be provided with automatic gauge control or like means for the last pass to keep the roll gap of the last pass at a desired constant value if the spring of the stand is sufficient to Warrant it.

The ideal setting for the penultimate pass is that which causes stock to be presented to the last pass having such a cross-section compared with the roll gap of the last pass that stock of the desired cross-section is discharged from the last pass.

FIGURE 6 illustrates a multi-stand rod mill having a very simple form of control. Such control is suitable if the space between the stands is small compared with the overall length of the rod being rolled. A rod 14 is shown first entering controlled penultimate stand 15 and then entering last "stand 16. If the spring of stand 16 is sufficient to warrant it, this stand may be provided with automatic gauge control or like means to keep the roll gap at the desired constant value. The rolling planes of stands 15 and 16 are mutually perpendicular. A gauge 17 of known form measures the width of the rod leaving stand 16. This measurement together with the desired width setting is fed into a differencing circuit 18 of known form and any Width error is presented to a control circuit 20 arranged to adjust the screwdown of stand 15. The ideal setting for the stand 15 is that which presents rod to the stand 16 having such a cross-section compared with the roll gap at this stand that the rod of the desired cross-section is discharged from stand 16.

FIGURE 7 illustrates a multi-stand billet mill provided with the form of control of the invention. A billet 21 is shown passing through stands 22, 23, controlled penultimate and adjustable stand 24 and last stand 25. The rolling planes of successive stands are in mutually perpendicular planes. If the spring of stand 25 is sulficient to warrant it, this stand may be provided with automatic gauge control or like means to keep the roll gap at the desired constant value. A gauge 26 of known form and measuring billet height and width may be located between stands 23 and 24 or between stands 24 and 25. A further gauge 27 of known form measures height and width of the billet being discharged from stand 25. A controller is shown at 28 and into this is fed: the actual billet height and width from gauge 27; the billet height and which from gauge 26; the required finished size of the billet, and information relating to the nominal size of the material prior to rolling, the

diameter of the rolls of the stands 24 and 25; the spread coefiicient of the billet. The output from the controller is presented to the stand 24 for adjustment of the roll gap at that stand.

With each rolling sequence, there is associated a set of correct values for the dimensions of the billet leaving each stand. To produce an accurate billet discharging from stand 25, the deviations of the height and width of the material entering the stand 24 (i.e. rolled by stand 23) as measured by gauge 26 in its full line position can be compensated by making a deviation from the correct nominal setting for the roll gap at stand 24. These deviations from the nominally correct values must obey a relationship which may be represented by a linear equation in which the mathematically weighted values of the errors in height and width of the material entering stand 24 and the deviation in the screwdown setting of stand 24 sum to zero or a constant value. The controller 28 is arranged and constructed to predict (or calculate) the value of the screwdown deviation in order that the relationship shall be obtained. The weighting of the errors may be determined empirically but, in the preferred method of application, they may be updated or corrected by observing, with the use of gauge 27, errors that occur in the billet that issues from stand 25. By means of a mathematical regression analysis technique using these errors, the weighting of the errors in height and width of the billet entering stand 24 and the correction to be made to the roll gap at this stand may be adjusted so that errors in the billet discharging from stand 25 are eliminated. The controller 28 which performs the calculations for corrections and for up-dating the control correction equations may take the form of a digital or analogue computing machine of known type.

As an alternative, the technique of the controller illustrated in FIGURE 5 may be used. In this case, the gauge 26 will be in its dotted line position and the errors measured will be those that enter stand 25, and the screwdown actuation of stand 24 is such that the weighted sum of the deviations in height and width sum to zero or a constant value. Corrections to this weighting may be made as previously described, use being made of gauge 27.

The ideal setting for the stand 24 is that which presents a billet to the stand 25 having such a cross-section compared with the roll gap at this stand that the billet discharged from stand 25 has the desired cross-section.

With the exception of a simple feedback correction system, the methods of dimensional control disclosed herein depend on their being zero, or constant, tension in the stock between the last and penultimate stands. Any variation in this parameter will have an eifect on the relationships illustrated in FIGURES 1 and 2. Techniques for avoiding interstand tension by allowing loops to form between stands are developed for rod and bar, and the operators of continuous (billet) mills have techniques whereby they control mills to maintain a condition of negligible interstand tension.

It will, of course, be appreciated that the discussion and disclosure of control systems given herein is by way of example only.

I claim:

1. A method of rolling stock in a mill for producing stock having a desired final cross-section in at least two passes comprising the steps of:

moving the stock through a mill stand in a penultimate pass; controlling the roll gap during the penultimate pass to produce stock having a predicted intermediate cross-section for presentation during the last pass;

moving the stock through a mill stand in a last pass;

and

fixing the roll gap during the last pass at a predetermined value which will roll stock of said intermediate cross-section into stock having said desired final cross-section.

2. A method as described in claim 1 wherein the passes are carried out in a stand of a reversing mill.

3. A method as described in claim 1 wherein the passes are carried out in a multi-stand mill.

4. A mill for producing stock having a desired final cross-section in at least two passes comprising:

means for moving the stock through a mill stand in a 60 penultimate pass;

means for controlling the roll gap during the penultimate pass to produce stock having a predicted intermediate cross-section for presentation during the last pass; 65 means for moving the stock through a mill stand in a last pass; and means for substantially fixing the roll gap during the last pass at a predetermined value .which will roll stock of said intermediate cross-section into stock having said desired final cross-section.

5.dA mill as described in claim 4 including reversing stan 6. A mill as described in claim 4 wherein said mill is a multi-stand mill.

7. A mill as described in claim 4 including means for 7 8 measuring a cross-sectional dimension of the stock dis- References Cited ghggiigolflggaslald penultimate pass in order to produce UNITED STATES PATENTS s. A mill as described in claim 4 including means for 2,012,706 8/1935 Biggert 72229 measuring a cross-sectional dimension of the stock dis- 5 3332084 2/1966 Suns 72 16 charged from the last pass in order to produce a control 3148916 5/1966 Kenyon et a1 7212 signal- MILTON s. MEHR, Primary Examiner 9. A mill as described in claim 4 including means for measuring a cross-sectional dimension of the stock discharged immediately upstream of the penultimate stand 10 72229; 234 in order to produce a control signal.

US. Cl. X.R. 

